In a small bowl, combine all the black eyed pea salsa ingredients. Do this first so the flavors have time to marinate and meld, and the red onion can lose some of its sharp bite.
In another bowl, whisk together cornmeal, flour, baking powder, salt, and pepper. Stir in Cheddar and scallion. In a 2-cup glass measuring cup, whisk together buttermilk, egg, and oil. If you don't have buttermilk, add any milk to the yogurt and stir to combine first, then add the egg and oil.
Add the wet ingredients to the dry and stir to combine. (In one test, I beat a leftover egg white to soft peaks and folded it into the batter. Would be delicious with or without!)
Heat a large skillet over medium-high heat. Add butter and swirl to melt and coat pan. Use a ¼-cup measuring cup to scoop batter into pan for 6 pancakes. Cook 2-3 minutes per side. I usually work in batches: 3-4 pancakes in the first, 2-3 in the second.
Top 3 pancakes with the sour cream and black eyed pea salsa. Save remaining pancakes for another meal, a snack, or a side.